Many automotive vehicles have rear wheel drive. Additionally many automotive vehicles with rear wheel drive have selective four wheel drive capabilities which are actuated upon operator command or automatically actuated in response to a slip condition of the powered rear wheels of the vehicle. To provide four wheel drive capabilities in the vehicle, there is provided a transfer case 7 (FIGS. 1-6). The transfer case 7 is typically provided at an output of the vehicle's transmission (not shown). The transfer case 7 often has an outer housing provided by front 10 and rear 12 shells boltably connected to one another. A front axle output shaft 14 is bearingly supported in the front and rear shells 10,12. A front axle output sprocket 21 is torsionally connected on the front axle output shaft 14. A main input shaft 22 is bearingly supported directly or indirectly by the front and rear shells 10,12. The main input shaft 22 has a radial shoulder 24 providing a stop. The main input shaft 22 is torsionally connected with an output shaft of the transmission of the vehicle (not shown) and rear axle (via a prop shaft and differential) of the vehicle (not shown). A first thrust bearing 26 is provided. The first thrust bearing 26 has a race 28 on its front end that is adjacent the radial shoulder 24 on the main input shaft 22. A main sprocket 30 is provided that is rotatably mounted on the main input shaft 22 by a bushing 31. The main sprocket 30 has an axial front side positioned against a rear race 29 of the first thrust bearing 26. The main sprocket 30 also has a radially inward axially rearward extending extension 64 having a splined outer diameter surface 70. The extension 64 also has a rear axial face 68. A chain 72 is provided which torsionally connects the main sprocket 30 with the front axle output sprocket 21.
A clutch housing 74 is provided having a generally radial portion 76 with a central splined opening 78 torsionally connected to the main sprocket axial extension 64. Typically the clutch housing 74 is fabricated from non-heat treat hardened steel. Clutch housing 74 also has an internally splined axially extending skirt 86.
A hub 90 provided spline connected to main input shaft 22. The hub 90 is axially moveable on main input shaft 22 and is generally axially aligned with the clutch housing skirt 86. The hub 90 has a splined outer diameter surface 88.
A clutch or friction pack 102 is provided having a first plurality of friction members 85 torsionally connected to the clutch housing skirt 86 via the clutch housing skirt's splined inner diameter 87. The first friction members or plates 85 are axially intertwined with a second plurality of friction members 89 spline connected with the hub 90's outer diameter 88. The friction members 85 and 89 are typically provided by metal plates coated with friction material intertwined with uncoated metal plates. The friction member 85 often can have a radial width significantly less than the radial width friction members 89.
A pressure plate 120 is provided spline connected to the hub outer diameter 88 to selectively compressively activate friction pack 102. A first ball ramp 121 is spline connected to the main input shaft axially spring biased away from the pressure plate 120. A second ball ramp 123 is provided for axially displacing the first ball ramp 121 to cause the friction pack 102 to torsionally connect the main input shaft 22 via the hub 90, friction pack 102 with the clutch housing 74 and main sprocket 30 and chain 72. The above connection torsionally connects the front axle output shaft 14 with the main input shaft 22.
The axial movement of the pressure plate 120 causes an axial reaction force against the friction pack 102 forcing the hub 90 against the radial portion 76 of the clutch housing 74. The clutch housing 74 is typically fabricated from a non-heat treat hardened stamping. Accordingly an outer radial portion of the hub 90 will wear into the clutch housing. To avoid the cost associated with heat treating the clutch housing 74, the clutch housing 74 is shielded by a heat treated hardened steel flat plane thrust washer 77. The clutch housing radial portion 76 has upended tabs 75 (FIG. 4) that locate the flat plane thrust washer cut outs 79 (FIG. 5).
To minimize rattle, a front face 91 (FIG. 6) of the thrust washer 77 should axially abut a rear inner face 93 of the clutch housing in a near perfect flat flush manner. Therefore sprocket extension 64 is purposefully axially rearward a distance 94 that is less than an axial thickness 95 of the clutch housing to ensure that the flat thrust washer 77 is flush against the front face 91. The above noted arrangement unfortunately ensures an oil pressure leakage path 96 for the pressurized lubricant forming from passage 105 in the main shaft between the front face 91 of the flat thrust washer and the rear axial face 68 of the extension. Additionally the full axial width of the clutch housing splined opening 78 cannot be torsionally engaged with the main sprocket axial extension 64. Torsional connection is further limited by a lead in chamber 103 on the splined outer diameter surface 70 on the sprocket extension 64. The lack of total engagement of the clutch housing splined opening 78 reduces the ultimate force transmitting capacity of the clutch housing.
It is desirable to provide a transfer case similar to that as described above wherein the flat thrust washer 77 positioned between the clutch housing 74 and the hub 90 is eliminated. Elimination of the flat thrust washer 77 not only lowers the cost of the transfer case but also eliminates opportunity for rattle and noise generated by the thrust washer. Additionally, elimination of thrust washer eliminates the aforementioned lubrication leakage path from in front of the flat flush washer 77 and the splined hub. Elimination of the thrust washer also simplifies fabrication of the clutch housing 74 since the clutch housing is delivered from any requirement to have the locking tabs 75 that keep the flat thrust washer 77 in position. Additionally the flat thrust washer 77 does not have to be staked in position to retain its position during transfer case assembly.